Carcinogenesis will be studied in urothelium from biopsies of human and rat bladders and in organ cultures. We have a plentiful supply of normal human bladder tissue and have already demonstrated the maintenance of normal human urothelium in vitro in organ culture for up to 3 months. We aim, 1) to produce neoplastic transformation of organ cultured rat and human urothelia in vitro with known bladder carcinogens and their metabolites, and also with the direct acting carcinogen methylnitrosourea; 2) to compare the ability of rat and human urothelia to metabolise carcinogens to active intermediates; 3) to compare the rates of formation, nature and quantity of macromolecular adducts formed with such carcinogens in the two species; 4) to define morphological, cytological and biochemical markers of neoplastic transformation of the urothelium for both species in vitro; 5) to compare the effect of promoters such as saccharin and tryptophan and of antipromoters such as retinoids on previously initiated human and rat bladder organ cultures. Tissues will be cultured by the techniques already developed here. Pilot biochemical studies already performed will be extended and will involve treatment of urothelia with radio labelled carcinogens and intermediates, isolation of adducts and assay by HPLC. Morphological evidence of transformation, particularly development of pleomorphic microvilli, will be monitored by scanning electron microscopy plus conventional histology and transmission electron microscopy. Cytokinetic studies and karyotype analysis will be used plus electron microscopy. Cytokinetic studies and karyotype analysis will be used plus cytology of the incubation media as developed here. Changes in alkaline phosphatase activity associated with neoplasia will be studied by cytochemical techniques. Evidence for malignant change will be checked by xenotransplantation into the immunosuppressed mouse host we have already developed. This programme should determine whether rodent and human urothelia metabolise and are similarly transformed by known initiators and promoters of bladder carcinogenesis. This will indicate whether the rat is an appropriate model for screening human baldder carcinogens and whether data obtained in the rat can be extrapolated either qualitatively or qualitatively to man. If the two species differ markedly, the potential value of organ cultures of human bladder will be emphasized. New knowledge and information obtained about such potential carcinogens as the arificial sweetners will be of immediate use.